This invention relates to techniques of etching a copper foil or copper plate, and more particularly to an etching solution or etchant for roughening a surface of a copper foil or copper plate so that the surface has acicular protrusions, a method for roughening a copper surface and a method for producing a printed wiring board in which a defect such as a pink ring or the like can be prevented from occurring and the number of manufacturing steps can be reduced.
A multi-layer printed wiring board has been conventionally made by laminating an inner layer material, an outer layer material and prepregs on each other. A copper-clad laminate on which a copper foil is laminated is used as the inner layer material and the like. In general, manufacturing of such a multi-layer printed wiring board is carried out in such a manner that the copper-clad laminate is subjected to a pretreatment such as a rust prevention and the like (preliminary treatment prior to circuit formation); the copper-clad laminate is then subjected to patterning and the like to form a copper conductive pattern layer (circuit formation); a roughening treatment is conducted to roughen a surface of the copper conductive pattern layer which is an inner layer material; an outer layer material such as resin, a film, ink or the like is laminated on the roughened surface of the inner layer material or copper conductive pattern layer to form a laminate (laminating); and the laminate is formed with through-holes and then subjected to electroplating.
As shown in FIG. 1, the preliminary treatment prior to the circuit formation generally includes removing a rust preventive film, washing with water, micro-etching, washing with water, rust preventing, washing with water and drying. The surface roughening as described above is executed by any one of a first process of forming a layer of copper oxide such as cuprous oxide or cupric oxide on the surface of the copper conductive pattern layer (blackening process), a second process of reducing such a copper oxide layer as described above to metallic copper using a reducing agent while keeping the configuration of the oxide layer (reducing process) and a third process of forming a metallic copper layer of coarse particles on a copper conductive pattern layer by electroless plating of copper (electroless copper plating process).
When the first process is employed, the following treatments are carried out sequentially: alkali degreasing, washing with water, acid degreasing, washing with water, micro-etching, washing with water, predipping, blackening, washing with water and drying. When the second process is employed, the following treatments are carried out: alkali degreasing, washing with water, acid degreasing, washing with water, micro-etching, washing with water, predipping, blackening, washing with water, reducing, washing with water, rust preventing, washing with water and drying. Further, when the third process is employed, alkali degreasing, washing with water, acid degreasing, washing with water, micro-etching, washing with water, predipping, catalyst provision, washing with water, catalyst activation, washing with water, electroless copper plating, washing with water, washing with acid, washing with water, rust preventing, washing with water and drying (see FIG. 1).
Unfortunately, the first process encounters a serious problem. More particularly, copper oxide is generally dissolved in acid. Thus, when the copper oxide of the copper conductive pattern layer is exposed on an inner surface of the through-holes due to formation of the through-holes, dipping of the copper conductive pattern layer in an etching solution or etchant during the subsequent electroplating causes the copper oxide to react with sulfuric acid in the etchant, to thereby be dissolved in the form of copper sulfate in the etchant, resulting in a defect called a pink ring occurring on the conductive pattern layer.
The second process needs to carry out reduction of the copper oxide to metallic copper after formation of the oxide, leading to an increase in the number of steps in the process. Also, it has another disadvantage of causing an increase in manufacturing cost of a printed wiring board because a reducing agent for the reduction is expensive. The third process likewise increases the number of steps.